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and renders the liquid turbid, is removed by adding a dehydrat-

ing agent.

Dehydration. Moisture can be readily removed from liquids
by adding a solid hygroscopic substance which does not act
chemically upon the liquid. The common
dehydrating agents are calcium chloride,
potassium carbonate, sodium sulphate
(anhydrous), quicklime, &c. Alkalis can-
not "of course be used for dehydrating or-
ganic acids, nor can calcium chloride be
employed in conjunction with alcohols or
organic bases, with which it combines. In
the present instance it can be used. A few
small pieces of the granulated or fused.
calcium chloride are added to the liquid.
The flask is corked and left to stand for
some hours until the .liquid becomes
clear. It is then distilled. A ther-
mometer is inserted into the neck of
the flask with the bulb just below the
side tube. The flask is attached to a con-
denser and heated gently on the water-
bath, so that the liquid distils at a moderate speed (2 — 3 drops
a second). The temperature is noted and the portion boiling at
35™43° collected in a separate flask. This consists of ethyl
bromide which may contain a little ether. Yield 75 — 80 grams.

FIG. 44.



H2S04 = C2H6.H.S04 + H3O.

~              Ethyl hydrogen sulphate.

C2H5.H.S04 4- KBr == C2H,Br + KHSO4.
Ethyl bromide,         ,
Properties— Colourless liquid ; b. p. 38 '8° ; sp. gr. 1*47 at 15^
(see Appendix, p. 234).
Determination of Specific Gravity.— A simple method
for determining the specific gravity of liquids is as follows: A
pyknometer, or small glass bottle, is used of about 20 to 30 c.c.
capacity, with narrow neck, upon which a mark, is etched and
which is closed by a ground glass stopper (Fig. 45).
The bottle is thoroughly cleaned and dried by warming and
aspirating air through it, after which it is allowed to cool and
weighed. It is then filled with the liquid, which is poured in